KR20090123887A - Electronic security for a power supply - Google Patents

Abstract

The invention relates to a security circuit for a power supply feeding a DC system. According to the invention, the security circuit is disposed on the outlet of the power supply, and a switch element (S1) is disposed between the positive power supply clamp (3) and the positive output clamp (1) towards the DC system, and a choke coil (L1) that is disposed between the switch element (S1) and the positive output clamp (1). Said choke coil (L1) is connected to an output capacitor (C2) on the side connected to the positive output clamp (1), and the side of the choke coil (L1) that is connected to the switch element (S1) is connected to the cathode side of a diode (D1) that is connected in parallel to the output capacitor (C2). Said security circuit also comprises a control for the switch element (S1), connecting the switch element (S1) in accordance with the power measured in the security circuit.

Description

ELECTRONIC SECURITY FOR A POWER SUPPLY

The present invention relates to a protection circuit for a power supply for supplying power to a DC system according to the preamble of claim 1.

In switch-mode power supplies, the current limiter is almost always integrated with the power semiconductor and coils to provide protection. Due to this current limiter, when the output power is distributed to multiple arms for protection using fuses or automatic cutouts, the necessary trip current cannot be delivered in the event of a short circuit. Electronic protective cutouts with precise overload characteristic curves and precise tripping currents are already in use. However, these circuits are complex because a very large amount of leakage power is formed in the switch elements of the protective cutout due to the heavy load.

Thus, for example, it has been proposed in the prior art to limit the loads to types which draw only small starting overcurrents and thus keep below the pulse leakage power of the current-limiting switches operating during the starting phase in linear mode. Mostly pulsed linear operation steps (5 to 200 ms) mean that the leakage power cannot be dissipated from the transistor quickly enough so that the thermal capacity of the transistor accepts only leakage current. Thus, a silicon chip with a thickness of about 100 μm and a surface of several square millimeters can only accept a very limited range of energy.

Thus, it has also been proposed in the prior art to relocate the leakage power into additional resistors that are controlled through separate transistors and thus allow a fairly large size to be used for energy reception. Due to the requirement to implement any given protective cutout setting values (adjustable protective cutout), only 75% of the energy can be accepted by the resistor when the largest leakage power occurs. Thus, transistors must be able to cover the remaining 25% with their thermal capacity. Such circuit arrangements are known from WO 02/082611.

In order that the load current does not exceed predeterminable limits, in each case the multiple power resistors and electronic switches in series correspond by selecting the correct combination of transistors in which the overall resistance between the load and the power supply is switched on and switched off. To be achieved by graduation.

The problem faced by all existing electronic protective cutouts is that they are installed at an unknown distance from the power supply. This means that the design of the protective cutout must take this distance into account and the load current increases when the loads are connected. The active arm must be placed on a positive line (eg + 24V) and the 0V connection of the load must be made through completely separate paths in space, as in loads of the car, for example connected to ground through the bodywork, where Only the + 12V line is switched. Clocking circuits are not possible because the 0V connection of the load is never routed to the point of cutout. Pulsing current flows through the 0V connection of the entire system, which leads to ground bounces and faults in the modules and loads.

A further problem arises in a slow starting car or during the connection of heavy loads, for example charging of load capacitors (eg the input of a DC / DC converter). The problem is that in industrial controllers a number of loads are used on the 24V control voltage (magnetic valves, processor modules with their DC / DC converters, capacitors connected in discharged state, starting DC motors, filaments Firstly, such as fluorescent lamps that need to be heated) arise from the fact. Many of these loads have a characteristic of temporarily drawing a current higher than the rated current when switched on. The use of switched-mode power supplies means that a negative aspect of these components emerges. The modules rarely deliver significant short currents on the output. When the rated currents of the power supplies are exceeded, the current limit runs with almost no delay and as a result the output voltage drops. This generally means that the entire control system is "crashed." If you want to continue using switched-mode power supplies, the only option is to limit the current of the individual loads to a value that exceeds only the power consumption planned for this load in the system plan. In this case, the power of the switched-mode power supplies is generally selected in the system scheme based on the sum of the expected individual consumers (loads) and the simultaneous generation of said individual consumers and the power type is selected accordingly. The fact that the maximum current is limited to one load and the maximum current lies slightly above the rated current if necessary and within the planned total energy consumption of the system causes a slower start up of these loads. Thus, the motor accelerates more slowly, the capacitors charge more slowly, the incandescent lap light can be darker, and so on. These delays are not critical to system functions in most cases, but the system planner should consider. The obvious main advantage is that the supply of the control voltage (eg 24V) is no longer interrupted when the consumer is connected and the system is not interrupted.

This soft start requires that the differential energy between the supply source and the product of the current and load voltage allowed by the load must drop at the switch element. For example, when the capacitor is charged, the result is that at the first instant the switch element exhibits a short circuit and the product of the voltage and current set must drop completely at the switch element. Such a switch element may be a resistor or more preferably a variable resistor, or may be a semiconductor operating like a variable resistor. Due to the corresponding large capacitors, the energy to be converted into heat in the switch element (or resistor) can be very large and soon exceeds the capabilities of the transistor.

It is therefore an object of the present invention to avoid these drawbacks and to implement a protection circuit for a power supply that powers a DC system, which represents a low cost option for implementing an electronic protective cutout, in particular in a DC output circuit of rated power supply.

These objects are achieved by the features of claim 1. Claim 1 relates to a protection circuit for a power supply for supplying power to a DC system, said protection circuit being proposed to be arranged at the outlet of the power supply and a switch element between the positive power supply terminal and the positive output terminal towards the DC system. And a choke is connected between the switch element and the positive output terminal, the choke having a side connected to the positive output terminal connected to an output capacitor and a side of the choke connected to the switch element being the output A diode is connected in parallel to the capacitor, and a control is provided for the switch element to switch the switch element in accordance with the current measured in the protection circuit.

The circuit arrangement is known as a buck converter. By using the inventive arrangement of the proposed protection circuit directly at the outlet of the supply source (e.g. 24V power supply), heavy loads such as motors that are slow to charge or start up of the load capacitors (input section of the DC / DC converters) The problem of switching on these components can be solved with very low overall costs in the components. By using the circuit arrangement of the present invention, switching of the total difference energy between the supply source and the load is not necessary. However, it is necessary to integrate the protection circuit of the invention in a power supply or to install the protection circuit very closely to a power supply provided at least the same electrical conditions.

It is an advantage that in the circuit of the invention, by incorporating one or more buck converters directly at the outlet of the supply power supply, short circuits in the system to be provided can be prevented. Each switching-mode buck converter in this case requires a stable supply voltage which is preferably supplied by the capacitor in order to eliminate the operation-related necessary pulse streams. In this case the switch transistor often cuts off the power supplied from the supply source to provide the magnetized choke with an opportunity to reduce the current again. In this case, the choke with current fluctuates around the output current value. The peak-to-peak value of the varying current is called ripple, and the average value of the choke current is ultimately the output direct current.

The diode connected to the choke provides automatic protection against negative voltages when switching off large inductive loads or when switching off the supply.

According to claim 2, the protection circuit can be integrated in the housing of the power supply, in which case the input capacitor of the protection circuit can also represent the output capacitor of the power supply. In this way one component can be saved.

However, optionally according to claim 3 the protection circuit can be implemented as a separate module for direct connection to the power supply. In this way the circuit arrangement of the invention also functions as a power divider.

According to claim 4, a protection circuit can be implemented as a separate module for connecting from a power supply to a remote power supply, wherein a separate 0V line is provided intimately with the power supply and protection circuit and with filters for smoothing pulse streams. Are provided as feedback. Suitable filters for smoothing the pulse streams are known in the art.

Claim 5 provides that the switch element is controlled via a microprocessor. In this case one signal can be transmitted from the control computer at regular intervals and, as will be explained in more detail below, the signal informs the individual outputs of each effective current-limit value. When the power is replaced, for example in the event of a fault, automatic adjustment can be made by simply entering the device address.

As an alternative to using chokes, claim 6 provides for the use of simple registers. Once again the protection circuit is placed at the output of the power supply and the resistor is connected in series with the switch element between the positive power supply terminal and the positive output terminal towards the DC system. The resistor is further connected to the output capacitor on the side connected to the positive output terminal. In addition, a control is provided for the switch element which in turn switches the switch element in accordance with the current measured in the protection circuit. Although suitable as a protection circuit within the environment of the present invention, this embodiment does not represent a preferred variant.

Claim 7 relates to a circuit arrangement with at least two protective circuits of the invention having at least two positive output terminals as power and output channels for powering a DC system.

Thus, multiple outputs, also referred to as output channels below, can be integrated into the housing, so that they are powered from the same power source. In this case, for example, when switching on the output channels, synchronization may be provided to reduce the load on the input capacitor to the protection circuit corresponding to the output capacitor of the power supply and thus corresponding to the general ripple of the outlet of the supply power.

According to claim 8, inputs for activating and deactivating output channels may be provided. This makes it possible to use electronic relays.

In the case of multiple output channels, a single microprocessor may be provided according to claim 9 to also control the switch elements of the at least two protection circuits.

Claim 10 enables analog circuitry to be provided for controlling switch elements of at least two protection circuits. The use of analog circuitry to control the switch elements is also possible when only one channel is provided.

According to claim 11 an integrated part of a control of a circuit of a power semiconductor and a power ASIC is provided.

According to claim 12, a hybrid circuit is provided, said hybrid circuit comprising power semiconductors and a coil of buck converters and preferably manufactured and installed as one module.

Claim 13 relates to a method for controlling a protection circuit, wherein the rated current value is predetermined and the switch element is operated only after a predetermined duration in which the rated current value is exceeded in the protection circuit. Current values exceeding the rated current value are referred to as overcurrent. The time until the operation of the switch element and thus the triggering of the protection circuit depends on how much the predetermined rated current value is exceeded. This time also depends on how the overcurrent is related to the rated current value and can be as long as the overcurrent is smaller than the rated current value.

The operation of the switch element to trigger the protection circuit may also depend on the thermal situation of the power semiconductors and other components of the current path. In this case, time values can be calculated by measuring the temperature or by measuring only the ambient temperature and the power curve history.

The output terminal assigned to the protection circuit is deactivated after a predetermined time when the current limit value exceeding the rated current value is additionally predetermined and the current-limit value is exceeded in the protection circuit. Is provided. The limited current value duration in turn depends on the predetermined rated current value and the smaller the rated current value can be, the longer. The operation of the switch element once again to trigger the protection circuit can also be dependent on the thermal situation of the power semiconductors and other components of the current path.

Claim 15 is provided to cause an output terminal assigned to the protection circuit to be deactivated when the input voltage of the protection circuit is not reached. Thus, when the input voltage of the protection circuit is not reached where the input voltage of the protection circuit corresponds to the output voltage of the supply power supply, the corresponding overload output is switched off, ie the output of the load overloads the power supply by overcurrent. Thus, the power supply proceeds in the current-limiting mode so that the output voltage of the power supply drops. The power supply thus goes back to normal mode and again supplies the rated voltage, for example by implementing multiple outputs. For linear regulators the system is already described in EP 1 236 257.

Claim 16 relates to the use of a buck converter as a current-limiting protection circuit at the output of a power supply which finally powers a DC system.

The invention will be explained in more detail below on the basis of an exemplary embodiment with the aid of the accompanying drawings.

1 shows a prior-art circuit arrangement.

Figure 2 shows a preferred embodiment of the protection circuit of the invention in the stage of operation in which the switch element is closed.

FIG. 3 shows the protection circuit described in FIG. 1 in an operating stage with the switch element open.

4 shows a typical system structure when the protection circuit of the present invention is used.

A circuit arrangement according to the prior art using analog current limiting is shown in FIG. 1, power supply terminals 3 and 4 are shown and output terminals 1 and 2 are shown on the right side. The output terminals 1, 2 are connected to the load side DC system. The switch element S1 is provided as a current-limiting element, but this switch element is not operated in the switching mode. In the current limit the switch element S1 must proceed in a semi-through-connected state, so it is assumed between the input voltage (+ 24.1V / 0V) and the load voltage (+ 24V / 0V). This forms a large leakage current in the switch element S1. The time limit should therefore be adapted to the heat capacity of the switch element S1.

2 shows a contrasting of a preferred embodiment of the protection circuit of the invention in the stage of operation in which the switch element is closed. 3 shows the protection circuit in the operating phase with the switch element open. The protection circuit of the present invention for a power supply for powering a DC system is arranged on the outlet side of the power supply. A switch element S1 is provided between the positive power supply terminal 3 and the positive output terminal 1 for the DC system and also a choke is provided between the switch element S1 and the positive output terminal 1. On the side connected to the positive output terminal 1, the choke L1 is connected to the output capacitor C2. The side of the choke L1 connected to the switch element S1 is connected to the cathode side of the diode D1.

During the operation of the positive output terminal 1, the switch element is shifted from the switching-off state to the switching-mode state. The output current can be determined by the slow increase in the pulse duty ratio to the permanently switched on state. This output current can be measured at the resistor R1 operated as a shunt, so according to the measured output current, the duty ratio of S1 is influenced with the help of the control unit (not shown in FIGS. 1-4). Receive. Diode D1 is designed only for short periods of operation and is therefore generally not cooled. The switch element S1 will be a semiconductor switch, preferably a MOSFET. When MOSFETs are used, depending on the type used, the heat sink can also be omitted.

The switch element S1 is in the switching mode only for a short time which is switched on, which means that switching losses also occur only at this stage. Since the transistors are already available at a very low resistance in the middle, a heat sink is no longer required for an ambient temperature of 60 ° C and output currents of 10A. Since the current flows continuously through the choke L1, the choke must conduct thermally during this period. However, due to the short startup phase of 50 to 500 ms, there is no need to dissipate additional losses through high frequency operation over a long period of time. Choke L1 may be implemented as an air-core reactor for a correspondingly high high frequency, simply including a winding without a core. The one component is generally made of copper lacquered wire. Due to short-term operation, ferrite chokes can be equipped with a high-permeability core, although they have high re-magnetization losses. Noise-suppressing chokes in the form of bar-core or mushroom-core are components of this type. These chokes do not have closed cores because these cores can be made simpler and better. This allows smaller size and lower permanent conduction losses to be achieved since the use of the ferrite core means that the number of wire windings is much smaller. The general capacitor for supplying the power supply voltage to the input part is omitted because the capacitor function is performed by the output capacitor of the power source corresponding to the input capacitor C1 of the protection circuit.

The current can be measured by resistor R1 in front of the electronic fuse. Optionally, register R1 may also be directly connected to the output line of the protection circuit. This direct connection has the disadvantage that uncontrollable currents flow at the switching-on moment in the buck converter section because the output capacitor must first be charged before current flows to the load. Instead of shunt resistors, the current can also be measured through a compensated DC converter such as a hall converter.

If an attempt is made to completely skip the resistor R1, the voltage drop at the switch element S1 can also be measured. If a MOSFET is included, a nearly linear relationship of current versus measurable voltage drop is established. However, the temperature of the transistor has a big influence on this relationship. Due to the known transistor temperature, the actual current (analog or digital) can be calculated via the compensation circuit. However, the evaluation of the current is difficult at the high clock frequency of the switch element S1, since the lower measured values (during the switching-on time of the switch element S1) are the total supply voltage (the switching-off time of the switch element S1). Because it changes at high frequencies. The clock L1 represents a further alternative for current measurement and this alternative is done with the RC element in parallel with the choke L1 which is characterized by a time constant much greater than the periodic duration of the clock frequency in the case of current limiting or starting. This causes the ohmic voltage drop of choke L1 to be measured and supplied to the controller as a setpoint value. The dependence of the choke L1 resistance on temperature is likewise formed. If the temperature of the choke L1 is known, compensation can be made as with the voltage drop measurement of the transistor. In addition, current can be measured with so-called sense FETs, which are MOSFETs featuring a separate current sensor output that can be evaluated.

The function of the circuit arrangement of the present invention is discussed below. Initially the current is measured in the resistor R1 and if it exceeds the rated current value, the switch element S1 is opened. During the switching-off phase of the switch element S1, the choke L1 has the opportunity to reduce the current because it transfers energy to the load. Because the current flow through the switch element S1 is interrupted, the current also does not flow through the input capacitor C1 and the resistor R1. Therefore, input capacitor C1 must be in a position to deliver current pulses. However, this is only necessary at the moment of current limiting of the same output during switching-on and therefore during charging of the output capacitor C1 and possible load capacitors at the output, and during operation of the current-limiting mode. Current limiting is timely limited and prevents feedback as a result of the connection of modules when the system is operating (so-called hot plugging) or overcurrent and thus voltage drops on the supply rail (24.1V / 0V) Use to do

At the start of the next period the switch element S1 is switched on again. The current ramp is predetermined during switching on to perform the current limit. In applications that are simpler and less known, better protection is to predetermine a current ramp that increases in power while meeting the maximum current limit. For loads that suddenly occur, such as switching on DC / DC converters, any intrusion of the output current will rarely occur, and this may be the case with any current ramp. As an alternative to the two methods, the current limit can only be used for control so that the circuit does not consider the voltage at the output. The switch element S1 is switched on from the operation of the output until the current of the current sensor does not exceed the maximum value. Then it is switched off and switched on again in the next period.

Figure 4 finally shows a typical system structure for the use of an electronic protection circuit according to the invention, the arrows showing the current path at a constant load. The 0V supply to the electronic protection circuits is only used to power internal electronics in this case. The loads are connected to 0V through separately routed lines. Most of these connections are not at the same time as the electronic protection cutout. The current limit must operate linearly because otherwise pulse streams in a switched-mode system induce uncontrolled current flows in the system and this current flow induction causes a ground bounce. This ground bounce is a result of, among other things, the inductance of the cables and lines, since large loops and therefore large inductances are mostly included.

It is noted that the circuit arrangement of the present invention is also suitable for detecting wire breaks by any available charge of the output capacitor C2 through a high resistance resistor from a higher voltage (eg, 26V). If the output increases to a value of, for example, 2V specified by the manufacturer above the value of the supply source, there is certainly no load, and thus wire breakage can be inferred. In addition, it is conceivable to provide an analog signal to the high resistance "protected" outputs as an imaginary part of the current so that the operator can only measure the actual current using the voltmeter. Holes may be provided in the circuit board for this purpose and contact may be provided to the tinned surfaces on the circuit board.

With the aid of the circuit arrangement of the present invention, a protection circuit is implemented for a power supply that powers the DC system, which protection circuit is a low-cost option for implementing electronic protection cutouts, particularly in the DC output circuit of the regulated power supply. Indicates.

Claims (16)

As a protection circuit for a power network supplying a DC system, The protection circuit is arranged at the outlet of the power supply and a switch element S1 is provided between the positive power terminal 3 and the positive output terminal 1 toward the DC system and the choke L1 is connected to the switch element ( Is provided to be connected between S1 and the positive output terminal 1, the choke L1 is connected to an output capacitor C2 on the side connected to the positive output terminal 1 and the switch element S1. The side of the choke L1 connected to) is connected to the cathode side of the diode switched in parallel to the output capacitor C2, and the switch for switching the switch element S1 according to the current measured in the protection circuit. In which a control unit for element S1 is provided, Protection circuit. 2. The protection circuit according to claim 1, wherein the protection circuit is integrated into the housing of the power supply, and a power output capacitor C1 represents an input capacitor of the protection circuit. Protection circuit. The circuit of claim 1, wherein the protection circuit is implemented as a separate module for connecting directly to the power supply. Protection circuit. The circuit of claim 1, wherein the protection circuit is implemented as a separate module for remote connection from a power source to a power source, wherein a separate 0V line is provided in close proximity to the power source and the power source for filters for smoothing pulse streams. Provided as feedback, Protection circuit. 5. The microprocessor according to claim 1, wherein a microprocessor is provided for controlling the switch element S1. Protection circuit. As a protection circuit for a power supply that powers a DC system, The protection circuit is arranged at the outlet of the power supply, a switch element S1 is provided between the positive power supply terminal 3 and the positive output terminal 1 toward the DC system and a load resistor is provided to the switch element S1. ) Is provided between the positive output terminal 1 and the load resistor is connected to the output capacitor C2 on the side connected to the positive output terminal 1 and measured in the protection circuit. In accordance with the present invention, a control unit for the switch element S1 for switching the switch element S1 is provided. Protection circuit. A circuit arrangement having a power supply for supplying power to a DC system and at least two protection circuits according to claims 1 to 6. The circuit arrangement has at least two positive output terminals 1 as output channels, Circuit arrangement. 8. The system of claim 7, wherein inputs are provided to activate and deactivate the output channels. Circuit arrangement. 9. A method according to claim 7 or 8, wherein a single microprocessor is provided for controlling the switch elements S1 of the at least two protection circuits. Circuit arrangement. The method of claim 7 or 8, wherein an analog circuit is provided for controlling the switch elements S1 of the at least two protection circuits. Circuit arrangement. 11. A method according to any one of claims 7 to 10, wherein an integrated portion of the power semiconductors and the circuit control portion is provided in the power ASIC, Circuit arrangement. 12. A hybrid circuit is provided, wherein the hybrid circuit comprises power semiconductors and buck converter coils and can preferably be manufactured and installed as a module. Circuit arrangement. A method for controlling a protection circuit according to any one of claims 1 to 12, The switch element S1 is operated only after a predetermined period of time when the rated current value is predetermined and the current is less than the predetermined rated current value. Method for controlling the protection circuit. 14. The output terminal according to claim 13, wherein a current limit value exceeding the rated current value is additionally predetermined, and after the predetermined time of the current-limit value is exceeded in the protection circuit, the output terminal assigned to the protection circuit. (1) is deactivated, Method for controlling the protection circuit. 15. The method according to claim 13 or 14, wherein when the input voltage of the protection circuit drops below a threshold, the output terminal 1 assigned to the protection circuit is deactivated, Method for controlling the protection circuit. Use of a buck converter as a current-limiting protection circuit at the output of the power supply to power the DC system.

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